To me, its 50-60 percent. (or 5 to 6 out of 10).
Which leaves games in their 60's to be barely struggling above mediocrity, games in their 70's to be a better than average, and games in their 80's to be "good", and then games in their 90's to be "excellent".
p.s. And nobody should ever review games with an out-of-10 system,
imo. Because 10/10 means 100% perfect which isn't right. No game should ever be 100% perfect. There is always atleast
something you can do to improve something. Even Angelina Jolie ;p So with just a 10 point system, it leaves you with 9/10 being the highest mark, which doesn't leave room for stuff being a wee bit better or a wee bit worse. In other words, if you play something absolutely amazing, and give it 9/10, and then you play another game that is even better, you don't really have anywhere higher to go. Or if you play something else which is amazing too, but not quite as good... then it means you can only really give it an 8, which isn't very good. So theres just not enough fine tune-age. (Unless you use decimal points, in which case, you mayaswell just use percentages).